Is a Dolphin a Fish?

A dolphin is a small toothed whale: warm-blooded, air-breathing, and a mammal in every respect, however fish-shaped it looks. There are about forty species, from the familiar bottlenose to river dolphins in the Amazon and the Ganges. The Greek word behind it, *delphis*, is related to *delphys*, the womb — the ancients had noticed that this sea creature gives birth to live young.

• A small toothed whale with a beaked snout. *A pod of dolphins followed the boat.*
• A mooring post or buoy for ships (nautical). *The tanker was tied to a dolphin.*
• Dolphin fish — an unrelated fish, better known as mahi-mahi. *Dolphin on the menu means the fish.*

Word forms

How it is used in a sentence

• Dolphins can recognise themselves in a mirror.One of the classic tests of self-awareness.
• The label says dolphin-friendly tuna.A claim about fishing nets, not about the fish inside.
• A dolphin surfaced beside the ferry.Surfacing is the giveaway: it has to breathe.

Dolphin or porpoise?

• Dolphin — longer beak, cone-shaped teeth, curved dorsal fin, often playful near boats
• Porpoise — blunt head, spade-shaped teeth, triangular fin, shyer
• Whale — the wider family; dolphins are part of it
• Pod — the word for a group of any of them
• Echolocation — how all of them find food in dark water

Through Old French *daulphin* from Latin *delphinus*, from Greek *delphis*. The French royal title Dauphin comes from the same word by a long detour: a noble family used a dolphin on its coat of arms, and the name stuck to the heir to the French throne.